What Causes Milky White Cloudy Aquarium Water?

Guppies in the aquarium

Milky white cloudy aquarium water is often just temporary. Poorly rinsed gravel in a new aquarium can cause white cloudiness. Restarting the filters after a shutdown can cause debris and tiny air bubbles to create a white haze. Adding supplements such as bacteria, pH adjusters, or calcium can also create a temporary milky white haze in the water.

All of these sources of white cloudiness are usually just temporary, lasting only a few hours to a few days.

If the cloudiness persists, it is likely caused by bacteria growing at rates that turn the aquarium water milky white. This kind of fast bacteria growth is usually the result of excessive organic waste within the fish tank.

Causes for milky white aquarium water:

  • The aquarium is new and bacteria are settling. These nitrifying bacteria are needed as they make the water safe for fish by converting highly toxic ammonia to the less toxic nitrate (see ‘The Nitrogen Cycle‘ for more info). During the initial stages of a new aquarium setup bacteria and waste levels will not be balanced, often resulting in milky white cloudy aquarium water.
  • The bacteria colony has been disturbed by environmental changes i.e pH or temperature fluctuations or by anti-bacterial medication. Re-establishing of the colonies can cause the water to turn white.
  • Larger additions of fish or livestock can cause bacterial colonies to multiply every 20 minutes in an effort to convert the additional organic waste being produced. The re-balancing of the biological balance will require some time. Again the result can be milky white cloudiness.

With growing bacteria in the aquarium, oxygen can be depleted. To solve the problem, correct any of the above mentioned causes. Most common are the addition of livestock which causes dangerous spikes on organic waste.

Algone will clear and prevent cloudy water by removing organic and inorganic waste. Algone will also minimize ammonia and nitrite spikes and lessen their highly toxic effect on fish and other livestock.

Check out Algone here

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Paul chaunt

I just setup a freshwater tank for tropical fish possibly chiclids I have crush coral for gravel it’s 39 gallons and big enough filter it’s white milky cloudy water now I read I possibly didn’t rinse gravel enough should I put in something for the cloudy water if so what or should I let the filter keep running to see if it clears thank you Paul

Since it’s a newly set up aquarium, it’s likely just fine dirt particles from the gravel. The filter should pick it up and clear it within a day, give or take.


I have a 100 gallon tank set up and it contains 2 Oscars and a Pleco. I have had this tank set up for about 5 months and have had no issues except the Ph is having issues staying at 7. Most of the time it is about 6. But about 8 days ago my tank started getting cloudy and milky looking……I changed out 25% of water…..and it started to clear up…slowly….then a few days ago I came home and it was getting very cloudy again…As of today it is extremely cloudy….tank is 18″ wide and it was so bad… Read more »


The pH plays a major role in this issue, because the bacteria converting waste to ammonia/ nitrite/ nitrate (beneficial bacteria) will be severely inhibited in their function starting at a pH of 6.5
With lower pH levels especially 6 and lower, the bacteria will cease their function altogether. Once the pH goes up again, a bacteria bloom can occur. as the bacteria try to re-establish the colonies. It is that bacteria bloom that turns the water milky white.
First things first, fix the pH problem. We have a great overview including actual cases from hobbyists listed on https://www.algone.com/adjust-ph-aquarium


i recently bought a 75 gallon aquarium. i filled the tank yesterday and today ist too cloudy. i added aquarium salt and white marvel chips. is it due to adding of those chips or nitrogen cycle process? can you help?

Since the tank was just set up, this is likely just substrate particles floating in the water. The filter should remove these and clear the water in just a day or two.


Hi i have a 20 gallon tank for two aquatic frogs thag I just cleaned a few days ago, washed the rocks and rinsed off the little log and plant I have it there. The first day it looked clean and clear but now (the third day) the water looks foggy and milky like it is dirty again already. This is the second time I have cleaned this tank and the first time I cleaned it, it did not look like this. The tank was clear for about three weeks so that is why I am worried that it is… Read more »


If you clean the aquarium too thoroughly, you wipe out the bacteria needed for the aquarium to provide a healthy and safe environment for the fish/ frogs. In essence, you are cycling the aquarium over and over. Here is a good maintenance plan that should make things much easier: https://www.algone.com/aquarium-maintenance-tips-and-fish-care-guidelines

Valerie Martin

My tank water is lime green and the water is making my bedroom smell really bad. Its the water in the tank what should I do

This is quite vague, so in a nutshell… make sure you are: 1. running an adequately sized aquarium filter 2. performing regular water changes 3. not overcrowding the aquarium with too many fish 4. not overfeeding your fish The green water is likely free-floating algae. Algae thrives in high nutrient water, particularly high nitrates. Nitrates are the result of decaying waste in the fish tank… uneaten fish food, fish poop, etc… Accumulating nitrates are due to too much waste entering the tank, a lack of maintenance, or both. Good aquarium maintenance practices are essential for a healthy aquarium, as are… Read more »

Mark P

We moved my fish tank downstairs and cleaned it out and everything got a new filter rinsed the rocks and everything and then the water got white and cloudy so we cleaned it again and it happened again. Not sure what’s happening


That would be a bacteria bloom. Bacteria, which make the water safe for the fish, settle anywhere in the aquarium. The filter is a preferred location because of, among others, the higher oxygen supply. Replacing the filter will also displace the bacteria. Cleaning has the same effect. If you see a slimy area, that is the protective coat of the colony. Just rinse the filter if it needs cleaned. Adjust the filter outlet, or lower the water level to the point where the filter outlet creates waves. This will ensure proper oxygen levels. You can wait this out, or use… Read more »


Hello I have a five gallon tank that I am setting up for a betta. I thought I washed everything thoroughly before putting my water in with my betta water conditioner. It got cloudy about two days in, and now has been cloudy for 3 days. I have a filter, heater, gravel, and a digital thermometer in it so far, haven’t put decorations in it yet. What should I do? Should I wait it out or just restart?


Some conditioners can cloud the water especially if they claim to have bacteria in the mix. You can wait this one out and read up on the following in the mean time.

Krystian Borja

Hi i have a 15 gallon aquarium it has not been cycled and i added new fish. The fish for what i see is ok and it is eating. But the water is cloudy. What should i do?

Just feed sparingly and perform a modest water change of about 15% of water every 5 – 7 days. This should keep nutrients lower and ease the effects of the aquarium break-in on your fish. Once sufficient beneficial bacteria are established, the tank should clear up on its own. Otherwise, consider an aquarium water clarifier such as Algone.

Guy Hanna

I have a brand new 65 gallon Aquarium. I rinsed off my gravel and set everything up for my fish. It is still foggy white, Is it my gravel or just that it is new?

Yes, it’s likely just from the gravel. If it persists for more the a couple of days, it may be a bacterial bloom. One post below, Thilo explains this to another aquarium keeper as follows: Bacteria that grow ahead of the beneficial bacteria can grow at speeds that turns the water cloudy. This is referred to as a bacteria bloom. No danger for as long as the aquarium is well oxygenated, as most are just by water surface movement. Bacteria blooms can occur if, the aquarium is newly set up, fish have been added, the bacteria got disturbed by either… Read more »


I have a 54 gallon tank. It’s been set up for bout 3months now. I decided to do a GLOW FISH TANK. It was touch and go for awhile …getting the water just right. Anyhow I have been able to add fish over time but now my water is very cloudy…took the water to have it checked and all was good except the ph was a little acidic but said not dangerous so we put the ph adjuster in it…please help ,,,do I just let it run it’s course….

Bacteria that grow ahead of the beneficial bacteria can grow at speeds that turns the water cloudy. This is referred to as a bacteria bloom. No danger for as long as the aquarium is well oxygenated, as most are just by water surface movement.
Bacteria blooms can occur if, the aquarium is newly set up, fish have been added, the bacteria got disturbed by either to intense cleaning, filter changes, changes in live stock, or medication (antibiotics). You can use Algone to speed up the process of clearing the water, or wait it out.


I have a 30 gallon tank i recently did my yearly full clean of the tank and cleaned the rocks its murky white, and its getting worse. The water is more white after a fewe days.

This sounds like a bacterial bloom, which is not uncommon for newly setup aquariums. Since you did a full cleaning, your tank will have to re-cycle, and you may experience what’s called New Tank Syndrome.

In any case, feed sparingly and avoid any big water changes. Your tank needs a chance to balance and any big changes will only delay that balancing. With time, the water should clear up on its own. If the problem persists, add Algone to your filter.

debbie hollis

Hi the water in the fish tank was a brown colour and smelly what was wrong with the water

That may indicate you are experiencing an algae bloom.

Read more here:

Description of Common Aquarium Algae
Aquarium Algae Control
Nitrate Control is Algae Control

Ayush sinha

I have made a 20 gallon aquarium before 2 days ago and yesterday when I added water to my aquarium the water remains cloudy. I have very less amount of gravels they are unclear. I have cleared the gravel but water remains hazy and I have only 2 fish, one red cap and koi carf, they also have produced lots of waste in this new aquarium. Please help me to remove cloudy water.

The cloudy aquarium water is likely just particles from the gravel that haven’t yet settled, or you are already experiencing a bacterial bloom. A bacterial bloom is caused by an imbalance of nitrifying bacteria in the fish tank. This is not unusual for a new aquarium. Avoid any big changes such as large water changes, or the addition of any new fish at this time. This should clear up as the aquarium establishes a healthy biological balance. Also see ‘New Tank Syndrome‘ for more information.


This changes has Influence in my red cherry shrimp tank. Temperature, Ph and hardness is good for these Nitrate & Ammonia is low but i dont konw what happend in my tank 🤔

My aquarium has turned yellowish color I’ve done 3 water changes plus added water conditioner and bacteria I still can’t get my tank to clear I had my water tested and my levels are all out of whack nitrates we’re 200 I have never had a problem with my tank until I added new stones I did wash them really well so I don’t know what to do other than take all my fish out and start over any suggestions

Yellowish water usually indicates the need for activated carbon. Check out our article about chemical aquarium filtration. My bet is that adding, or changing the carbon in your filter will clear up the aquarium water.


Do you have a drift wood in there? That might be the reason why the tank is yellowish.

Tabitha kirkhart

My 28 gal nano cube has been set up with seahorses since november it went through its cycle very well. Has been pretty clear water the entire time but have been having a problen with film algea on my sand. I bought 2 small sand sifting starfish and a horshoe crab to help with the algea almost a month ago. It has been doing very well until yesterday when i came home my pumps were low on water and were kind of blowing out a bunch of small bubbles. I did a cleaning of my ornaments and sand only about… Read more »


Fine air bubbles can cloud the water, residues in the pump and pipes can have the same effect. Fine particles from the substrate is also an option. In any case, it should not persist for long and the water should return to normal. Other possibilities is a bacteria bloom. Bacteria are settling inside the filter in larger numbers than outside. If the filter water volume is reduced, some of the bacteria might no be working properly, or become dormant. Watch for possible ammonia spike. In addition and in consequence, waste is not processed efficiently and heterotrophic bacteria (the ones processing… Read more »

I set up a new aquarium. But I use some black& white gravel from a former tank. And few fish after it was two week up. Any way water turn pea green. Took my water to be tested was told given some Prime that detoxification the water. Later did 20% water change that didn’t help . So I Broke the tank down completely was everything throughout clean. Had a very clean tank. Now starting with my 3 fish out of 7 when I first started. Put the necessary water regiments for the water. By 2 week it is right back… Read more »


When you start an aquarium, the system will cycle. This in short means that bacteria settle to make the water safe for the fish. This also means that waste is not properly processed, and that waste can cause the water to turn green or white. This has little to do with the gravel selection.
When starting, keep the filters running, and make sure the water is well oxygenated. If you have fish, feed very sparingly. Make sure you follow a rigid regiment in maintenance.


First off all when I put the cycling stuff in the tank it was cloudy but only for a day or two. But now it’s got like a cloudy substance on the top of the water just floating is this meant to happen? If so why? How long will it last?

You’re best off contacting the manufacturer of the cycling product you used in the tank. They should be able to help you determine any side effects and further actions you can take.


Hello mate. That “Stuff” it’s just bio-film. Completely normal. Just use your filter to “wave” the surface of the water and you should be fine!


We started our new 10 gallon tank on Saturday. We purchased a 24 hour quick start conditioner, washed all of our decorations, gravel, etc. and set up the tank. 24 hours later we introduced 3 Mollies; woke up the next morning with 3 deceased fish and cloudy water. I’ve read about the bacteria bloom and figured I must have introduced the fish too soon to the tank. We ordered a bubbler to help oxygenate the water but we don’t know if we should install it now or wait until after the bloom has cleared? How long should we wait to… Read more »


Every aquarium needs to cycle, you can read more in detail using the following link:
In short, bacteria need to settle in order to make the aquarium safe for fish. This process can take 2-4 weeks to complete. During this time you will see spikes in ammonia/ nitrite, both can be fatal for the fish. Once both values return to 0 ppm with nitrates measurable, the cycle is complete, and you can add the fish of your preference.
To start the cycle you can use the no fish method https://www.algone.com/cycling-the-aquarium-without-fish or use starter fish (feeder fish)

Terri P

Even though Mollies are listed under “beginner” fish, the are too susceptible to water condition changes. Some good old male guppies, danios, or tetras would be better choices.

Jeffrey Cagle

I broke down my 10 gallon tank yesterday and cleaned everything with a strong bleach solution because my betta died of fin rot. I set it back up and it crystal clear. I added a small amount of gravel from an established tank with an undergravel filter to seed the fresh one with good bacteria. I also stuck a cotton swab in ammonia and swirled it in the water. This morning, the water was cloudy…GOOD! That means my tank is growing beneficial bacteria. The bacteria will settle into the gravel and filter in a few days. The water will clear… Read more »

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